All the clues are in

All the clues are in place. Dad came home and we ran the truck situation through and there are only a few possible answers for what transpired:
1) The car was not completely in Park and it slipped into neutral and slid down the driveway on its own. (signs for this: tire tracks did not turn nor slide down. there are obvious tread marks, not skidding sliding marks)
2)Steve or someone else got into my car and shifted it into another gear and let it do directly backwards. (this is improbably because Steve would tell me and he wouldn’t take my car in the first place and it wasn’t hotwired so nobody could have just started it to get it out of park)
3)It was on ice and slid backwards. (Signs against: only one back tire was most likely on an ice patch and this wouldn’t cause the entire car to roll down. Also, like I said, there were TRACKS, not sliding marks.)

This is a total mystery. We have no idea what in the world caused this phenomenon.
No, we are not haunted. Don’t even guess that.